In typical semiconductor single crystal manufacturing apparatuses by the CZ method, there is provided a crucible for containing a raw material melt within a growth furnace main body (sometimes referred to as a main chamber), and a heater is disposed around the crucible to melt the raw material within the crucible to immerse a seed crystal into the raw material melt while maintaining keep the temperature of the molten raw material melt constant to pull upwardly the seed crystal while rotating seed crystal and crucible in directions opposite to each other to thereby grow a semiconductor single crystal beneath the seed crystal. At this time, in order to efficiently perform heating of the raw material melt by the heater, and to protect the furnace walls of the metallic growth furnace main body from radiant heat of the heater, there are disposed insulating members made of such a material as graphite in the vicinity of the internal walls of the growth furnace main body. By those insulating members, it becomes possible to keep the heat inside of the growth furnace main body and to protect the furnace walls, and thus to suppress excess heating of the heater to keep the temperature of raw material melt constant without wastefulness.
Moreover, in recent years, in growth of semiconductor single crystals, particularly in growth of silicon single crystals serving as material of each silicon wafer used for manufacturing integrated circuits etc., it is necessary to grow a crystal in which grown-in defects internally introduced at the time of growing the single crystal have been suppressed so as to have an extremely low density because there is a tendency such that semiconductor devices formed at a wafer surface layer will be miniaturized more and more. In view of the above, there has been frequently used a method of disposing a graphite member such as a cooling cylinder and a heat insulating ring above the raw material melt to pull upwardly the crystal while controlling the cooling rate of the crystal with high precision.
However, in such a method of controlling the crystal cooling rate, there are many restrictions according to the growth condition, for example, the fact to suppress radiant heat delivered from the heater and the raw material melt to the crystal to be grown as small as possible, and the fact that formation precision of temperature gradient in the crystal pulling axis direction are required. As a result, there was a predetermined limitation for the purpose of increasing the pulling rate to improve productivity of growth of the single crystal. In particular, in the growth of large-sized silicon single crystal having a diameter exceeding 200 mm or 300 mm, it is necessary to fill raw material of 100 kg or more into a large-sized crucible to melt it thereafter to perform crystal growth while maintaining the atmosphere within the growth furnace main body at a temperature to 1400° C. or more. As a result, it is considered that the calorific value of the heater becomes large, and radiant heat from the heater constitutes an obstruction also at the time of cooling a single crystal pulled upwardly from the raw material melt so that cooling of the crystal is hindered, thus making it difficult to dramatically realize speeding up of the pulling rate.
Moreover, in order to pull upwardly a single crystal having a large diameter and a long constant diameter part as described above, there is also being made such an attempt to use an apparatus for manufacturing a semiconductor single crystal in which the growth furnace main body is enlarged and expansion of the space where raw material is disposed is performed. In this case, it becomes difficult to efficiently perform heat insulation of its internal space following enlargement of the growth furnace main body. Accordingly, it would be inevitable to increase heat amount of the heater for the purpose of holding a raw material melt at a high temperature in melting the raw polycrystalline material or at the time of growing a single crystal.
In view of the above, there is proposed a method of lessening heat outflow toward the lower part of the growing furnace by using a heat insulating plate.
For example, Patent Literature 1 discloses a single crystal pulling method of controlling oxygen concentration taken into a single crystal by changing the number of laminated heat insulating plates disposed below a crucible.
Moreover, Patent Literature 2 discloses a crystal pulling apparatus in which there is disposed a heat conduction radiation member for receiving radiant heat from a heater to transmit the heat by thermal conduction to a part below a crucible to discharge the radiant heat toward the crucible.
Further, Patent Literature 3 discloses a semiconductor single crystal manufacturing apparatus having a heat insulating plate disposed under a crucible and capable of performing vertical movement drive by a heat insulating plate lifting mechanism.